Deoiling of cracking furnace effluent



May 5, 1964 H. s. KIMBLE ETAL DEOILING OF' CRACKING FURNACE EFFLUENT Filed Dec. 12, 1960 United States Patent() t i 3,132,011 DEOILING F CRACKING FURNACE EFFLUENT Harvey S. Kimble, Tulsa, and Donald E. Griffin and .lohn

J. Moon, Bartlesville, Okla., assignors to Phillips Petroleum Company, a corporation of Delaware Filed Dec. 12, 1960, Ser. No. 75,364 4 Claims. (Cl. 55--40) This invention relates to deoiling of cracking furnace effluents. In one aspect it relates to deoiling of cracked gases resulting from cracking of ethane and of propane in the production of ethylene. In another aspect i-t `relates' to the removal trom cracking furnace etlluents of materials which tend to polymerize yand deposit on equipment surfaces.

The presence of polymerizable material in hydrocarbon cracking furnace eluents is well known in the hydrocarbon cracking art. Polymerizable materials react at elevated temperatures to produce polymers, some of which are liquid land some of which are solids. It is the solid polymer material which causes trouble and expense be` cause it deposits on such heat exchange equipment as reboiler tubes, and on the walls ot rebelle-rs yand fractional distillation columns, particularly in the kettle section thereof, in pipes and in other equipment contacted by fluids containing Ithese polymer forming materials. Coatings of solid polymer electively interfere with heat transfer thereby reducing the etliciency of the heat exchange equipment. In the cracking of ethane and propane for production of ethylene such polymerizable materials form.

It is one object of this invention to provide a process for the removal of oils containing the above-mentioned polymerizable material from cracking furnace ellluents.V Another object ot' this invention is to provide a process for removal of polymer-izable material from cracking furnace etlluents to eliminate solid polymer formation and deposition on heat exchange equipment. Still another object of this invention is to provide a process for removal of polymer-forming material from cracking furnace eluents resulting from the cracking of ethane and of propane in the production of ethylene. Yet another object of invention is to provide a process for removal of undesirable high boiling oils including aromatic and polymerizfable materials from ethane and from propane cracking furnace etlluents. Still other objects and advantages will be realized upon reading the following description which, .taken with the attached drawing,

feasible to send the cracking elluents from both the Y ethane and the propane cracking operations to the deoiler even if the deoiler had suicient capacity to handle both streams. Separate absorbers are used because the two cracking furnace ellluents have unlike compositions.

Since lthe absorption oil must be recovered from the rich absorbent from the ethane cracking effluent absorber and since this stream is small it is advantageously deoiled in the deoiler treating the effluent tro-m the propane cracking operation. Operating in this manner then permits recovery of absorption oil and removal of heavy materials from Iboth ethane and propane cracking effluents in a single deoiling and stripping operation.

Y The drawing illustrates in diagrammatic lform an arrangement of apparatus for carrying out the process and achieving the objects of this invention.

In the drawing reference numeral 42 Videntities a conduit leading trom a source of ethylene to apparatus 41.

This apparatus identied by reference numeral 41 illusice trates the processing of ethane which involves cracking of an ethane-containing charge stock, quenching the effluent of the cracking operation and compressing the quenched eflluent. Thus, the cracked, quenched, and compressed efuent from the cracking operation passes from apparatus `41 through ya conduit 7 into the lower portion of an absorber 8. This absorber is termed here- 'in heavy ends absorber. yIn this absorber a relatively small volume of an absorption oil enters the top of the absorber through a conduit 30 and flows downward in contact with up-owing vapo-tous or gaseous material from conduit 7. This heavy ends absorber is provided with efficient vapor-liquid contact promoting apparatus such as bubble cap trays. The volume of absorbent owing doWnw-ard through this `absorber is intended to be sufficiently small that it :absorbs mainly the heavy and high .boiling ends, that is, high boiling oils and the polymer-forming materials from the charge gases without substantial labsorption of Ithe normally gaseous materials. Eluent and unabsorbed gases trom absorber 8 leave this vessel by way of conduit 9 for subsequent treatment as desired.

A conduit l44 conducts propane from la source, not shown, to a system of cracking, quenching 4and compression identied Vby reference numeral 43. This apparatus 43 is quite similar to. that identied by reference numeral 41, the ditlerence being that the cracking furnace of apparatus 43 is designed for and operated under conditions suitable for the cracking of propane to produce ethylene; The eluent from the cracking, quenching,'the compressi-onsystem 43 is passed through a conduit 17 into the lower portion of an apparatus herein termed a deoiler and identified by reference numeral 18. The upper portion of this deoiler is actually an absorption column more or less similar to labsorber 8. This deoiler is provided with eiiicient vap r-liquid contactpromoting packing such as bubble cap trays. An absorption oil or absorben-t is introduced into the upper portion of deoiler 18 through. a conduit 29.- .Unabsorbed gases leave deoiler 1S through a conduit 28 for such disposal, as desired. In addition to the introduction of lean absorbent through conduit 29 into the upper portion of the deoiler 18, the rich absorbent from the bottom of absorber 8 passes through -a conduit 10 into the Vdeoiler at about its midsection, vertically. Thus this rich absorption oil from absorber 8 is mixed with the Vabsorbent introduced' through conduit Z9 and the combined liquid flows on down and into a reboiler section 11. reboiler section 11 involves the use of a reboiler heat exchanger 13 which heats the rich absorption oil from the lower portion of the reboiler section 11 and allows a portion of this heated rich absorption oilto pass through a conduit 1.4 into the lower portion of section 11. Thus the heated rich absorption oil re-entering the lowerportion of section 11 reboils this section of the column. The more volatile of the absorbed materials vaporized trom the V,absorption oil assists in stripping the light ends trom the.

downliowing combined absorbents flowing downward in sections 1-1 and 18. The downilowing absorbent in column 8 is intended to` absorb polymeric material formed during cracking of the ethane in apparatus 41 and the -downflowing absorbent in deoiler 18 is intendedto absorb substantially the same constituents from the propane cracking operation. -It is realized that other materials besides those desired tobe absorbed will be absorbed in such absorption equipment.

- In one modeof operation it is preferred to use only a very. small stream of absorbent in obsorber `8 so that substantially only the highestboiling constituents will be absorbed. -In deoiler 18 a suihciently large tlow of absorbent is introduced through conduit 29 as to act as a reux and cool the top of this deoiler to promote absorption and to assist in retarding loss of absorbent with the una-bsor'bed gases.

The bottoms from the reboiled absorber 11 leave this vessel via conduit 19 for passage into a depentanizer column 20. Heat for reboiling is introduced into this column by Way of a'conduit .35.Y This heat may be in the form of superheated steam passing through a heating coil, not shown, in the kettle section of column 20er outside the column as reboiler 13, or this heat can be in the form of open steam added directly into the kettle section of the column. Pentane and lower boiling materials are passed overhead through a conduit 26 from column 20, condensed in a condenser 27, said. condensate passing intoan accumulator tank 23. A valved conduit 34 communicates with the accumulator tank in case pressure reliefv is necessary. A portion of the condensate from accumulator 23 required for refluxing column 20 is passed through a conduit 33 into the upper section of the column while the remainder is passed through a line 22 as a product of the system, for such disposal as desired. The depentanized bottoms material from depentanizer 20 are removed therefrom through a conduit 21 and are passed into an absorption oil re-run still 32. This stilll is operated in such a manner as to distill overhead the absorption oil introduced subsequently through conduits 29 and 30 into the absorbers. In other words, still 32 is an absorption oil purification still. The vaporous absorption oil or absorbent is passed from the still through an overhead conduit 2S, the material is condensed in acondenser 36 and condensate is passed on into an accumulator tank 40. The condensate is pumped through a conduit 37 by a pump 38, the condensate or absorbent oil being cooled in a cooler 12 and chilled in a chiller 16 prior to introduction through conduits 29 and into the respective absorbers. Heat for reboiling the kettle section of still 32 is introduced thereinto through a conduit 39 from a source, not shown. Preferably steamfrom conduit 39 passes through a heat exchange coil in the kettle section of still 32 so as not to introduce water into the contents of the still. Bottoms product from still 32 is removed from the still through a conduit 24 for such disposal as desired. This bottoms material while identiiied in a table given hereinafter as C5+ is actually material boiling higher than the abas a coolant.

20. In this case the remainder of this bottoms material, that is from 90 to 50 percent is passed through conduit and added to the purified absorbent flowing through conduit 3'7. By distilling a substantial fraction of the depentanizer bottoms the concentration of high boiling polymers and polymer-forming materials in the depentanizer bottoms is maintained at a sufliciently low level and thus polymer formation on high temperature spots in this apparatus is maintained at a minimum.

Steam for heating reboiler 13 is passed thereto through a conduit 15 from a source, not shown. This reboiler is a closed coil heat exchanger for the purpose of maintaining the absorbent in substantially a moisture-free condition. A conduit 31 communicates with accumulator tank 40 for addition of make-up absorbent as required. InV one instance a benzene-rich absorption oil boiling from about 180 to about 360 F. was used as an absorption oil for this operation. This absorbent contained approximately weight percent benzene. In this case the absorption oil re-run still 32 was operated in such a manner as to withdraw bottoms material through conduit 24 having an initial boiling point of approximately 230 F. In one instance this bottoms. material had a boiling range of approximately 230 to about 432 F.

With the use of a benzene-rich absorbent with the removal of bottoms material from re-run still 32 having a boiling range of from about 230 to about 432 F. the temperatures andV pressures employed in the system are those illustrated inthe drawing.

Itis realized by those skilled in the art that the ternperatures given in the drawing can be varied within limits by varying the pressures at the various process points accordingly. v

Cooler 12 can, if desired, employ plant cooling water For further kcooling or chilling the effluent from cooler 12, a refrigerated cooler or chiller 16 is required. This. refrigerated chiller or cooler can involve use of a propane refrigeration cycle. An ammonia refrigerationsystem also can be used in place of propane if desired.

Thefollowing tabulation illustrates product compositions. at various process points of the system. The column headings in the table are found on the drawings as the corresponding reference numerals.

Pound Mols Per Hour Stream N0 7 9 10 17 2l 22 24 25 28 29 30 31 Component:

CHL- 309.0 308.0 0.2 1, 626. 2

CzH.. 823. 0 819. 5 3. 5 374.8

Calin. 16. 8 16.6 0.2 172. 2

Absorbent Oil 53. 5 117. 5

Total .3, 407. 4 3,448.1 130 3 4, 760. 8

Temperature, F 60 60 60 50 Pressure, lbs. 111.2 gage 112 116. 5

pentanizer 20. In. many instances it may be sutiicientV to distill-in re-run still 32 from, for example, 10 to 50 percent of the depentanized bottoms from depentanizer 65 Such auxiliary apparatus as valves, pressure indicating,

recordingqand control equipment, temperature indicating, recording and controlling equipment are not shown for purposes of simplicity and brevity. The need for such auxiliary equipment, its installation and maintenance are well understood by thoseskilled in the art.

VWhile the aboveow diagram has been described for illustrativey purposes, the invention obviously is not limitedV thereto. i

We claim: Y

1. A process for separating into different hydrocarbon fractions rst and second gas streams `of different comsteps of:

(1) absorbing heavier hydrocarbons from said first stream in an absorbent in a first absorption zone While leaving substantially all of the C1 and C2 hydrocarbons unabsorbed;

(2) passing said C1 and C2 hydrocarbons overhead as a rst overhead fraction while recovering rich absorbent containing heavier hydrocarbons as a first bottoms fraction;

(3) absorbing heavier hydrocarbons from said first bottoms fraction and from said second stream in an absorbent in a second absorption zone as a second bottoms fraction while leaving substantially all of the C1 and C2 hydrocarbons in said second stream unabsorbed;

(4) passing the C1 and C2 hydrocarbons of step (3) overhead as a second overhead fraction;

(5) separating said. heavier hydrocarbons from said second bottoms fraction to separately recover lean absorbent and heavier hydrocarbons;

(6) passing lean absorbent from step (5) to steps (l) and (3) as said absorbent; and

(7) recovering as products the first and second overhead fractions of steps (2) and (4) and the heavier hydrocarbons of step (5),.

2. The process of claim 1 wherein the gases contacted in said first and second absorption steps are gaseous effluents of hydrocarbon cracking operations and said absorbent is an aromatic liquid boiling within thejrange of about F. to 225 F.

3. 'The process of claim 1 wherein said lirst stream is an eluent from ethane cracking containing substantial proportions of ethylene, said second stream is an eilluent from propane cracking also containing substantial proportions of ethylene, and said absorbent is an aromatic liquid boiling within the range of about 175 F. to about 225 F. t

4. The process of claim 1 wherein said streams contain heavier hydrocarbons higher boiling and lower boiling than said absorbent; and step (5) comprises the steps of distilling the lower boiling hydrocarbons from said absorbent and thereafter distilling the lean absorbent from the residue.

References Cited in the le of this patent UNITED STATES PATENTS Kniel Oct. 30, 1951 

1. A PROCESS FOR SEPARATING INTO DIFFERENT HYDROCARBON FRACTIONS FIRST AND SECOND GAS STREAMS OF DIFFERENT COMPOSITIONS AND EACH CONTAINING SUBSTANTIAL PROPORTIONS OF C1 AND C2 AND HEAVIER HYDROCARBONS WHICH COMPRISES THE STEPS OF: (1) ABSORBING HEAVIER HYDROCARBONS FROM SAID FIRST STREAM IN AN ABSORBENT IN A FIRST ABSORPTION ZONE WHILE LEAVING SUBSTANTIALLY ALL OF THE C1 AND C2 HYDROCARBONS UNABSORBED; (2) PASSING SAID C1 AND C2 HYDROCARBONS OVERHEAD AS A FIRST OVERHEAD FRACTION WHILE RECOVERING RICH ABSORBENT CONTAINING HEAVIER HYDROCARBONS AS A FIRST BOTTOMS FRACTION; (3) ABSORBING HEAVIER HYDROCARBONS FROM SAID FIRST BOTTOMS FRACTION AND FROM SAID SECOND STREAM IN AN ABSORBENT IN A SECOND ABSORPTION ZONE AS A SECOND BOTTOMS FRACTION WHILE LEAVING SUBSTANTIALLY ALL OF THE C1 AND C2 HYDROCARBONS IN SAID SECOND STREAM UNABSORBED; (4) PASSING THE C1 AND C2 HYDROCARBONS OF STEP (3) OVERHEAD AS A SECOND OVERHEAD FRACTION; (5) SEPARATING SAID HEAVIER HYDROCARBONS FROM SAID SECOND BOTTOMS FRACTION TO SEPARATELY RECOVER LEAN ABSORBENT AND HEAVIER HYDROCARBONS; (6) PASSING LEAN ABSORBENT FROM STEP (5) TO STEPS (1) AND (3) AS SAID ABSORBENT; AND (7) RECOVERING AS PRODUCTS THE FIRST AND SECOND OVERHEAD FRACTIONS OF STEPS (2) AND (4) AND THE HEAVIER HYDROCARBONS OF STEP (5). 